1. Field of the Invention
The present invention relates to a coated workpiece packaged in a sealed enclosure comprising one or more barriers and getter agents in an enclosure substantially free of chemical contaminants for storage without loss of sensitivity, resolution or process latitude. More particularly, the present invention relates to a package for storing environmentally sensitive resist-coated mask blanks.
2. Description of the Related Art
Chemically Amplified Resists (CAR) are extremely sensitive to contaminants. In microelectronic device manufacturing, Chemically Amplified Resists are generally manufactured and used on site in controlled environments and tool sets. They are not packed for storage. In mask blank writing, the mask blank manufacturer coats the blanks with a Chemically Amplified Resist, generally in a mask shop, and ships them to a location where they can be exposed and subsequently processed into a mask. In such cases, packaging is of great importance.
One of the problems associated with the manufacture and shipping of resist-coated mask blanks has been the variability in the performance of the resist-coated mask blanks resulting from variable degree of contamination. Because the presence of a defect in the resist-coated mask blanks can not be detected by practical methods at an early stage, such defects do not surface until at a very advanced stage of use, i.e., after many hours of imaging and development work when degradation of the properties of the resist-coated mask blanks become obvious.
Proper storage of coated films of photosensitve materials is a common problem associated with humidity, heat, and solvent absorption. These effects are described, for example, in: (1) U.S. Pat. No. 6,120,983; (2) an article by H. Ito and M. Sherwood, J. Photopolymer Science and Tech., 12, 625–636 (1999), which discloses an investigation of a DUV resist by NMR including aspects of residual casting solvent and PAG decomposition in a film and storage effects; and (3) G. Czech, et al., Microelctronic Engineering, 23, 331–5 (1994), which describes the influence of DMF on profiles of chemically amplified resists. In addition, the chemically amplified resists are susceptible to absorption of amines and moisture, as described in an article entitled “Airborne Contaminants and Chemically Amplified Resist Stability” by W. Hinsberg, S. MacDonald, N. Clecak, C. Snyder and H. Ito, SPIE Proceed., 1925, 43–53 (1993). U.S. Pat. Nos. 5,985,524; 5,962,184; 5,861,231; 5,712,078; 5,585,220; 5,296,332 and 4,491,628 describe chemically amplified resist (CAR) based on acid catalyzed removal of acid sensitive resists containing acid sensitive functional groups, such as, t-butylesters, carbonates, acetals or ketals. Base sensitive resists are also known. Both type resists have been developed over the last twenty years as fast resists of high resolution for photolithography with doses of <50 mJ/cm2 and for electron beams in the range of <50 μC/cm2.
Fast and high resoltuion resists that are exposable by electron beams or laser beams at all wavelengths are also vital for next generation production of photomask blanks (see “Positive Chemically Amplified Resist for Next Generation Photomask Fabrication” by T. Segaw et al., SPIE Proceed., 3236, 82–93 (1999)). In this process, precoated plates of resist on chrome covered quartz are written by a laser or electron beam pattern generator. Precoated plates are generally received from a blank manufacturer.
Because the films of resist are very thin, i.e., <400 nm thick, a coated six inch square plate has only about 10 mg of resist which would be susceptible to microgram levels of absorbed acid, which may subsequently catalyze the deprotection reactions of the amplified resists. Thus for long term storage of the CAR resists, the storage environment should be free of even minute quantities of acids, particularly acids having a pKa<6, bases having a pKb<6, as well as solvents and moisture. Ambient air contains moisture and can also contain acid precursors, such as, sulfur dioxide (SO2) and nitrogen oxide (NO2), which are common contaminants in the environment occuring generally at ppm levels. For contamination caused by acid precursors, see J. Lynch, C. VanBowersox and J. Grimm, Environmental Science and Technology, 34, 940–9 (2000).
Prior art attempts to preserve chemically amplified resist (CAR) have involved providing a topcoat of polyacrylic acid, as described in an article entitled “Effect of Gaseous Peremeability of Overcoat Layer on KrF Chemically Amplified Positive Resists” by S. Kishimura, J. Sakai, K. Tsujita and Y. Matsui, J. Vac. Sci and Tech., B14, 4234–8 (1996), or filtering the contacting environment to remove ammonia and amines, as described in an article entitled “Development of Ammonia Absorption Filter and Its application in LSI Manufacturing Environment” by A. Saiki, et al., J. Photopolymer Science and Tech., 8, 599–606 (1995). In some cases, such topcoats have caused deteriorated performance (process scumming) and/or have introduced coating defects to the resist film, as described in the previously cited S. Kishimura, J. Sakai, K. Tsujita and Y. Matsui, J. Vac. Sci and Tech., B14, 4234–8 (1996). Filtration of the process air has been used to prevent “T-top” scumming during the post-expose bake, as described in previously cited W. Hinsberg, S. MacDonald, N. Clecak, C. Snyder and H. Ito, SPIE Proceed., 1925, 43–53 (1993) and A. Saiki, et al., J. Photopolymer Science and Tech., 8, 599–606 (1995). However, this approach has not been used with acidic vapors or under long term storage conditions.
U.S. Pat. No. 6,120,860 describes a package to store reactive liquid organic amines inside a bag. The package uses aluminzed nylon coated with polyvinylidene chloride. This patent does not make any reference to storage of a workpiece coated with a resist film that is sensitive to optical radiation, particulates or chemical contaminants, including outgassing acids, vapors and moisture. No getter agents are included in this package.
Acid catlyzed deprotection of radiation sensitive chemically amplified polyhydroxystyrene ketal resists used for mask-making and their storage is described in U.S. Pat. Nos. 6,043,003 and 6,037,097 and W. Huang, et al., “A CA Resist with High Sensitivity and sub 100 nm Resolution for Advanced Mask Making,” Proceedings of SPIE, Vol. 4066, pages 150–159 (2000). Attempts to preserve plates by packaging the coated plates in a single layer polymer package, i.e., a single plastic bag, are described in U.S. Pat. Nos. 6,043,003 and 6,037,097. However, this method is not adequately effective. For example, it is not effective aginst permeation of acidic or basic organic or inorganic vapors or potential outgassing acids, vapors and moisture from the packaging materials themselves, from the resist coated mask blanks or from the carrier or holder of the resist coated mask blanks.
None of the above references describe storage of environmentally sensitive resist-coated mask blanks without loss of sensitvity, resolution or process latitude in an enclosure substantially free of chemical contaminants. None of the above references substantially addresses the problem of variability in the performance of the resist-coated mask blanks resulting from variable degree of contamination. Because the presence of a defect in the resist-coated mask blanks can not be detected by practical methods at an early stage, such a defect does not surface until at a very advanced stage of use, i.e., after many hours of imaging and development work when degradation of the properties become observable. None of the above references has a solution to the problem of variability in the performance of the resist-coated mask blanks or suggests a method of producing reprodicible performance attributes. Thus, there is a great need in industry for means for reproducibly storing such coated films of photosensitve materials without loss of sensitvity, resolution, process latitude and performance.
It is highly desirable that plates coated with photosensitve materials should last at least three months and the resist should not change in dose to print or in linewidth more than about 5%. Furthermore, since the chemically amplified resist (CAR) films would be particularity sensitive to moisture and acid precursors, such as, SO2 and NO2, the physical or chemical removal of the vapors inside the package to store photomask blanks would be highly desirable for protection against infiltration of reactive vapors and outgassing contaminants.
Accordingly, it is the object of this invention to provide a packaged material, such as a coated chemically amplified or non-chemically amplified resist plate, a process for preparing such a packaged material and a method of storing such a material inside a package for a period of at least three months to preserve the sensitvity, resolution and performance thereof after such a storage